The long term objective of this research is to investigate the role of iron in asbestos-induced cancer. The mechanism by which asbestos causes cancer is unknown. However, asbestos catalyzes many of the same reactions that iron does and the most carcinogenic forms of asbestos can contain as much as 37% iron. This proposal is based upon the hypothesis that iron is responsible for some of the biological effects of asbestos. The iron may be active in or on the asbestos fiber, but mobilization of the iron may increase its reactivity with 02 resulting in greater toxicity and carcinogenicity. The specific aims are: 1) to determine whether iron is required for asbestos-catalyzed 02 consumption and 02 radical generation and determine the effect of iron mobilization on these two activities; 2) To determine whether 02 and iron are responsible for the DNA damage induced by asbestos in vitro and whether mobilization of iron from asbestos increases asbestos-induced DNA damage; 3) to determine whether iron in or on asbestos is required for asbestos-induced DNA damage, cytotoxicity, and transformation in Syrian hamster embryo (SHE) cells in culture; and 4) to determine whether iron can be mobilized from phagocytized asbestos in SHE cells and whether this mobilization results in increased amounts of DNA damage, cytotoxicity, and transformation. Desferrioxamine B, which forms a redox-inactive chelate with iron, will be used to determine whether iron is required for asbestos-catalyzed reactions in vitro and biological responses in vivo. Using conditions established for mobilization of iron from asbestos, the -effect of mobilization on the reactivity of iron with 02 will be determined by measuring 02 consumption and by measuring the formation of -OH using ESR with spin trapping. To determine whether 02 is required for asbestos-induced DNA damage (single strand breaks and 8-OHdG) , asbestos and DNA will be incubated in the absence of 02. The role of 02 radicals in initiating DNA damage will be investigated by using specific inhibitors ( mannitol, ethanol) or protective enzymes (superoxide dismutase, catalase). To determine the effect of intracellular mobilization of iron on crocidolite induced DNA damage, cytotoxicity and transformation of SHE cells, cells will be treated with asbestos or asbestos followed by NTA, an iron chelator that can penetrate cell membranes and promote 02 radical formation.